The present invention relates to the art of tools and tool supports and, more particularly, to a support for drilling components and drilling tool defined thereby.
It is known in the art of drilling tools to combine a center drill with cutter blades providing radially extending cutting edges spaced axially behind the tip of the center drill. Such a combination is particularly useful in connection with the drilling and boring of metals by providing for the center drill to be of high speed steel and the cutter blades to be of a hard metal alloy such as tungsten carbide. In this respect, the high speed steel drill enables positive penetration at the center of the bore, and guidance during the drilling operation, and location of the carbide cutting edges axially outwardly of the axis of the drill optimizes the cutting capacity thereof. Such a combination drilling tool and the advantages thereof is disclosed in U.S. Pat. No. 2,294,969 to Engvall et al. A drill and the support for the component parts thereof according to the present invention finds particular utility in connection with the combination of a high speed steel twist drill and carbide cutting edges and, accordingly, will be described in detail herein in connection therewith. At the same time, however, it will be appreciated that the present invention has broader application and is not limited to such combination of cutting materials. It is also known in the art of drilling and drilling tools to provide a drilling tool support on which a center drill and cutter blades having radially extending cutting edges are removably mounted to facilitate replacement or resharpening of the cutting edges. Examples of such drilling tool supports are disclosed in U.S. Pat. Nos. 1,499,584 to Litchfield; and, 3,712,753 to Manzi.
A number of disadvantages are attendant to the construction and use of such combination drills heretofore provided, and tool supports heretofore provided for removably supporting center drill and cutting blade components. In this respect, for example, considerable force is imposed on the radially extending cutter blades in a direction transverse to the tool axis during a drilling operation, whereby the rate of penetration and thus the drilling speed are limited, in part, by the structural integrity of the arrangement defining the support for the radially extending cutter blades. Heretofore, such support has not enabled optimizing the cutting speed with regard to the cutting characteristics of the materials of the drill parts, or has required structurally complex support arrangements requiring special machining operations which render the drill or tool support unreasonably expensive. Another factor affecting cutting speed is the ability to dissipate heat generated during the cutting operation which, in part, is related to the displacement of chips along the drilling tool. In this respect, the primary support portions of certain combination type drills heretofore provided are defined by structural modifications of standard twist drills having spiral lands extending therealong which are of a diameter equal to that of the hole being drilled or bored. Accordingly, chip removal is achieved by movement of chips along the spiral flutes between the lands. Such a spiral flute, together with the surface of a hole being drilled, provides a chip removal path which is of small cross-section and is longer than the axial distance between the cutting end of the drill and the point of chip discharge. Therefore, the chips, which are hot, are compelled to move along a long spiral path which is small in cross-section, whereby heat dissipation is at a rate much lower than desired. Heating is of course at a maximum at the point of cutting engagement between the drilling tool and the material being bored, and such heating as is well known affects the life of the cutting edges of the drilling tool components. Accordingly, it will be appreciated that the life of the cutting edges is further affected by trapping heat at the cutting end of the drilling tool which, in effect, is the result of a long chip removal path.
Efforts to minimize or overcome the disadvantages of such high temperatures at the cutting end of the drilling tool by the occasional introduction of a cooling lubricant either requires the withdrawing of the drill for introduction of the lubricant into the hole being drilled, or the introduction of lubricant into the flute area of the drill and the periphery of the hole being drilled during the drilling operation. The former is undesirable from the standpoint of operating time lost in order to achieve lubrication, and the latter is undesirable in that penetration of the lubricant to the cutting end of the drilling tool is minimal in that the lubricant is absorbed by the chips in the flutes and is influenced to flow outwardly of the bore along the flutes by the configuration thereof before reaching the cutting end of the drilling tool.
Further in connection with such combination drilling tools, considerable time can be lost in connection with the use thereof during a given drilling operation by having to remove the drill, resharpen or replace blade portions thereof, and then remount the drill and continue the operation. Moreover, considerable cost can be incurred in connection with removable and replaceable blade components having but a single useful cutting edge which can be damaged during use to the extent that resharpening of the cutting edge is not possible. This is especially true with blades of hard metal alloys such as tungsten carbide which is extremely brittle. Accordingly, when the one cutting edge becomes so damaged, the cutter component must be replaced or, if the blade is permanently secured to the tool support, the entire drill must be replaced. It will be appreciated that all of these characteristics increase tool costs and time required to achieve a given drilling operation and, thus increase production costs with regard to the drilling operation being preformed.